Method of producing superficial carbonization of metals and alloys



Patented July 25, 1939 UNITED STATES PATENT OFFICE METHOD OF PRODUCINGSUPERFICIAL CARBONIZATION LOYS OF METALS AND AL- poration of Delaware NoDrawing. Application March 5, 1937, Serial No. 129,193. In Great BritainMarch 27, 1936 12 Claims.

The present invention relates to a method of producing superficialcarbonization of metals and alloys, to an electrode constituted of suchsuperficially carbonized metals and alloys, and to an electron tubecontaining such an electrode.

It is well known that for various reasons, it has often been desirableto blacken a metallic surface. For example, it is known that in order tofacilitate radiation from a surface that surlO face should be blackened.A particular instance is that of an electron discharge tube, the gridand plate electrodes of which tend to heat up in operation and to bringabout undesired electronic emission. In order that the heat may beradiated as quickly as possible from such electrodes, it is of advantageto blacken their surfaces and various methods of rendering the surfacesblack by carbonization have already been suggested or attempted.

It is an object of the invention to provide an improved process ofproducing'a carbonized surface on a metal or alloy.

It is another object of the invention to provide an improved process ofc'arbonizing metallic strip 5 especially a strip used in thermionicdischarge tubes.

The invention also contemplates the provision of a method of carbonizingmetallic strip within the envelope of a thermionic discharge tube.

Other objects and advantages will become apparent from the followingdescription of a preferred embodiment of the invention.

According to the present invention a carbonized surface is produced onmetals or alloys by employing a carbon-containing metal or alloy andheating it in vacuum or in an atmosphere incapable of reacting rapidlywith carbon until a firmly adhering film of carbon is formed on thesurface.

The invention may be applied with particular advantage to the treatmentof nickel, but is not limited to the treatment of any particular metalor alloy.

For the purpose of giving those skilled in the art a betterunderstanding of the invention, the

following description is. given of a preferred embodiment of theinvention.

In accordance with the principles of the present invention, it isnecessary to co-ordinate the carbon content, the general composition ofthe material, the duration of the heating and the temperature to producea satisfactory deposit of carbon. In general, as the temperaturedecreases the time required to reach a given blackness of 65 carbonincreases and as the carbon content decreases the temperature to be useddecreases also. Thus, in the case of nickel the carbon content should beat least 0.1% and if it is as low as this the temperature should notexceed 650 C. on heating in vacuum. If, as is preferred, the car- 5 boncontent is 0.25% or 0.30% or over, the temperature may advantageously befrom 900 C. to 950 C. although it may lie anywhere between 500 and 950C. If the carbon content is as high as 0.5% temperatures up to 1200 C.may be em- 10 ployed.

The foregoing relationship between maximum allowable temperatures andcarbon contents may be approximately expressed algebraically by theequation where T is the temperature in degrees centigrade and C is thecarbon content in percent. The duration of heating varies as statedabove, but

as an example if a temperature of 850 C. were employed several hourswould be needed to produce a substantial carbon deposit even with afairly high percentage of carbon, (say 0.5%) Whereas only a few minutesare necessary if a temperature of 1000 C. is employed. Other factorsthat affect the duration of the heating are the nature of the heatingchamber and the surrounding atmosphere.

If the carbonized material is intended to be used in the construction ofelectrodes for elec- 30 tron discharge tubes, it may be treated inaccordance with the invention when in the form of strip, rod or wire, orafter it has been formed into an electrode, either before or afterassembly in the discharge tube. This discharge tube may have thestructure of a conventional thermionic discharge tube.

By way of example a suitable material which may be carbonized inaccordance with the invention and used for the electrodes of a dischargetube is nickel wire or strip comprising 0.35% carbon, 0.05% silicon,0.13% iron, 0.04% copper, 0.04% magnesium, a trace of manganese, and therest nickel. After heating this material in vacuum (for example, in anexhausted silica tube 45 placed in a furnace) at a temperature of about900 C. for 30 minutes, it will be found to have acquired a firmlyadhering deposit of carbon.

Instead of employing a vacuum during the blackening process, anatmosphere of nitrogen, 50 argon, helium or other gas incapable ofreacting rapidly with carbon may be employed.

In the manufacture of a discharge tube, the electrodes may be mounted inthe tube prior to the formation of the film of carbon. The enatmospheressuch as nitrogen, argon, helium, etc.,

The invention includes a discharge itube'em- 1 bodying an electrode witha blackened surface produced in any of the ways described above, andparticularly a discharge tube having the surfaces of all the electrodesexcept the cathode blackened as just described. Y

It is to be observed that the present invention provides a process inwhich a firmly adhering film of carbon is produced onlmetals .or alloysby employing a carbon-containing metal or alloy and heating it in vacuumor in an inert atmosphere until .a' proportion of ,the carbon isexpolled. In the claimswhere the expression in an atmosphere incapableof reacting rapidly with carbon" is used, it is to be understood asincluding within its scope not only inert gaseous but rarifiedatmospheres or vacuum as well. In

the -manufacture of a discharge tube, the'.elec'-. trodes may be mountedprior to the formation.

. out in an atmosphere incapable of reacting rapidly with carbon until afirmly adhering film of carbon is, formed on the surface.

2. The method of producing a carbonized surface on nickel, whichcomprises heating nickel containing at least 0.1% carbon at atemperature within'the range of about 500 C. tol200 C. in an atmosphereincapable ofreacting rapidly with carbon until a firmly adhering film ofcarbon is formed on the surface.

V 3. A methodaccording to claim 2 in which the carbon content of thenickel is 0.25% or over and the heating is conducted at a temperaturelying between 500 and 950 C. V

4. The method of producing a carbonized surface on a nickel alloy' forthe manufacture of electrodes for electron discharge tubes whichcomprises employing a carbon-containing nickel alloy containingsuflicient carbon to become car- "bonized, and heating it within thetemperature range ofabout 500 C. to about 500 C. plus 1400 times thecarbon. content in percent, said heating being carried out inanatmosphereincapable of reacting rapidly with carbon until a firmlyadhering film of carbon is formed on the surface.

5. The method of producing a carbonized surface on a nickel alloy whichcomprises employing a carbon-containing nickel alloy containingsuflicient carbon to become carbonized, and heating 'ly adhering film ofcarbon is formed on the surface.

' 6. The process of manufacturing an electron discharge tube comprisingmounting in the tube an electrode made of a nickel alloy containingsufiicient carbon to become carbonized, and heating the mountedelectrode at a temperature Within the range of about 500 C. to- 1200 C.in an at mosphere incapable of reacting rapidly with carbon untilafirmly adhering film of carbon is formed on the. surface.

7. A process as set forth in'claim 6 in which the electrode is .made ofnickel containing at least 0.1% carbon. 7

8. A process as set forth in claim 6 in which the electrode is made ofnickel containing at least0.25% carbon and the heating is conducted at atemperature between about 500 and about 9. A process asset forth inclaim 6 in which the electrode is made of an alloy containing about0.35% carbon, about 0.05% silicon, about 0.13% iron, about 0.04% copper,about 0.04% mag-v nesium, a trace of maganese and the rest substantiallynickel and the heating is conducted at about 900 C. for about 30minutes.

10. The method of producing a carbonized surface on nickel alloy, whichcomprises heating an alloy containing about 0.35% carbon, about 0.05%silicon; about 0.13% iron, about 0.04% copper, about 0.04% magnesium, 'atrace of manganese and the rest substantially nickel in vacuum at atemperature of about 900C. for about 30 minutes. toform a firmlyadhering film of carbon on the surface.

11. An electrode element having relatively thin cross-section composedof heat treated nickel or V nickel alloy containing carbon throughoutthe cross-sectionand having uncombined carbon occontaining about 0.35%carbon, about 0.05 sili r con, about 0.13% iron, about 0.04% copper,about 0.04% magnesium, a trace of manganese and the rest nickel, thecarbon being at least in part un'-"

